1. Field of the Invention
The present invention relates to a facsimile apparatus including a modulation system capable of operating in accordance with ITU-T Recommendations V. 8 and V. 34 and a communication method therefore, and more particularly relates to a facsimile apparatus and a communication method therefor capable of detecting a communication error occurring in V. 8 or V. 34 mode communication. The present invention further relates to a communication apparatus which includes the above facsimile apparatus and which operates with the above communication method.
2. Description of the Related Art
Various standards are defined for a facsimile apparatus under recommendation by the ITU-T (International Telecommunication Union--Telecommunication Standardization Sector). For example, the ITU-T Series T Recommendation defines terminal equipment and protocols for telematic services. Recommendation T. 4 defines Group 3 facsimile terminals and Recommendation T. 30 defines procedures for document facsimile transmission by Group 3 facsimile terminals over the general switched telephone network. The ITU-T Series V Recommendation for data terminal equipment defines procedures for data communication over the general switched telephone network. Recommendation V. 8 defines procedures for starting sessions of data transmission, Recommendation V. 21 defines a modulation system operating at a data signaling rate of 300 bit/s, and Recommendation V. 34 defines a modulating system operating at data signaling rates of up to 33600 bit/s.
A facsimile apparatus capable of operating in accordance with the ITU-T Recommendation T. 30, previously known as CCITT (The International Telegraph and Telephone Consultative Committee) recommendation, can communicate with any facsimile apparatus which is also operating in accordance with the ITU-T recommendation, even when each communicating apparatus is equipped with different modulation systems.
When a facsimile apparatus incorporating the modulation system defined in Recommendation V. 34 wishes communication with another facsimile apparatus, the apparatus is required to first operate, after the line is connected, in accordance with the start up procedures defined in Recommendation V. 8. Once it is indicated in the V. 8 start up operation that the modulation system defined in Recommendation V. 34 is available both in the transmitting and receiving terminals, then signals for each phase defined in Recommendation V. 34 are exchanged for determining line conditions, modem parameters and so on, so that the communication is carried out at optimum conditions. (Hereinafter, communication or operation in accordance with the procedures defined in Recommendation V. 8 or V. 34 is respectively referred to as V. 8 or V. 34 mode communication or operation.) The V. 34 mode communication is carried out either in the duplex or half-duplex mode using several tone signals and binary signals for different speeds.
FIG. 15 is a diagram showing an example of a typical start up signals sequence of a facsimile apparatus capable of V. 8 and V. 34 mode communication, from V. 8 mode sequences through V. 34 mode sequences, up to the end of facsimile handshaking and prior to starting control channel signals sequences.
In the drawing, TX is a transmitting terminal and RX is a receiving terminal. CM represents a call menu signal which is transmitted by the transmitting terminal to delineate modulation systems available at the transmitting terminal TX, ANSam a modulated answer tone signal which is transmitted by the receiving terminal RX in response to a calling tone from the transmitting terminal TX indicating that the line is connected, JM a joint menu signal which is transmitted by the receiving terminal RX in response to a CM signal to specify modulation systems available at both terminals, A a tone which is transmitted by the responding modem, B a tone which is transmitted by the transmitting modem, CJ a CM terminator signal which indicates detection of a JM signal and termination of a CM signal, and INFO0a and INFO0c respectively represent an example of signal for exchanging information of modem capability, result of line probing and data mode modulation parameter.
Exchanges of signals for the start up procedures in accordance with the V. 8 and V. 34 procedures are very complicated, and generally the communication is automatically carried out between the modulation systems at both sides, a transmitting side and a receiving side. Various modem parameters are determined by the communication between the modulation systems without involving control of the host CPU of the facsimile apparatus in which each modulation system is installed.
However, depending upon conditions of communication line, instances occur where transmitted signals do not reach the destination terminal, which is called hereinafter as a communication error, resulting in wasting of communication time.
FIG. 16 is a diagram illustrating an example of a communication error occurred in V.8 mode communication due to a fault in the line, and FIG. 17 a diagram illustrating an example of a communication error occurred in V. 34 mode communication. FIG. 16 illustrates a state that a joint menu signal JM from a receiving terminal does not reach a transmitting terminal TX in V. 8 mode communication and both terminals TX and RX are in a state to continue transmitting each signal.
FIG. 17 illustrates a state that an INFO0a signal from a receiving terminal does not reach a transmitting terminal TX in V. 34 mode communication and both terminals TX and RX are in a state to continue transmitting each signal.
In V. 8 mode communication, signals for establishing communications between TX and RX, such as CM, JM and CJ signals, are repeatedly transmitted until a valid response is received from the destination terminal. In V. 34 mode communication, certain signals are also repeatedly transmitted.
In addition, in V. 34 mode communication, if a valid response is not received for a predetermined period of time, a recovery sequence is initiated. In this recovery sequence, the communication process is repeated so that several previously transmitted signals that have received valid responses are retransmitted and the signal that did not receive a valid response is also retransmitted.
However, in the V. 8 and V. 34 Recommendations, there is no stipulation for terminating the communication to disconnect the line even if a responding signal as specified is not received within a certain period of time after transmitting a signal or starting the recovery sequence.
For a case that a communication error occurs, the ITU-T Recommendation T. 30 specifies that if a valid responding signal is not received from a destination terminal within a specified period of time, such as, for example, 35 sec, after transmitting a signal, the terminal may signal to the operator or disconnect the line.
A period of time waiting for receiving a response signal is called a time-out period and the expiration of a specified time-out period is known as a time-out in the Recommendation T. 30.
A facsimile apparatus is generally designed to disconnect the line if a time-out occurs in accordance with the T. 30 procedures. A facsimile apparatus including the modulation system capable of operating in accordance with the V. 8 and V. 34 Recommendations generally continues the V. 8 or V. 34 mode communication until a time-out occurs in accordance with the procedures defined in the Recommendation T. 30.
One drawback to repeatedly transmitting certain communication signals when communication cannot be established with a destination terminal is that a relatively long time may be spent before succeeding in the transmission or reception of a signal or before a time-out occurs in accordance with the procedures defined in the Recommendation T. 30. As a result, communication time is wasted, usually without an operator knowing it.